1. Field of the Invention
The present invention relates to a color flat panel display, and more particularly, to a spacer forming the spacing between electrodes of a color flat panel display.
2. Description of the Related Art
Recently, an electroluminescent display (ELD), a plasma display panel (PDP), a liquid crystal display (LCD) and the like have been developed as a color flat panel display. However, in comparison with a cathode ray tube (CRT) that uses an electron beam, the conventional color flat panel display bas not reached a satisfactory level in view of performances such as a luminance, a contrast and a color reproduction
To overcome the restrictions of the conventional color flat panel display (the ELD, the PDP and the LCD) and implement a high-quality image comparable to the CRT, there have been proposed an improved color flat panel display that is based on a screen scanning of an electron beam.
Meanwhile, Japan Laid-open Publications No 3-184247 and No. 3-205751 disclose an image display apparatus for displaying a high-quality image comparable to the CRT on a flat panel display that uses an electron beam, in which an image displayed on a screen is divided into unit cells constituting a matrix and then an electron beam is deflectively scanned to each unit cell, so that a phosphor screen is light-emitted to thereby display an entire color image.
FIG. 1 is a view of a conventional color flat panel display based on a screen scanning of an electron beam.
FIG. 1 is an exploded perspective view showing main elements of the conventional color flat panel display. Referring to FIG. 1, the conventional color flat panel display includes a rear glass 1, a rear electrode 2, a filament cathode 3, a control electrode 4, a signal modulation electrode 5, a focus electrode 6, a horizontal deflection electrode 7, a vertical deflection electrode 8, and a front glass 9, all of which are arranged one after another. In addition, the rear glass 1 and the front glass 9 are sealed to maintain a vacuum state.
In more detail, the rear electrode 2 is formed of a conductive material such as metal and graphite on a flat panel. The rear electrode 2 is arranged in parallel with the filament cathode 3 and a negative voltage is applied to the rear electrode 2 to thereby cause an electron emitted from the filament cathode 3 to be directed toward the screen.
Generally, the filament cathode 3 is formed coating an oxide cathode material on a surface of a tungsten wire. At this time, a plurality of filament cathodes are arranged to generate the electron beam constantly distributed in a horizontal direction.
As an electrode for drawing the electron beam 11, the control electrode 4 is spaced apart from the filament cathode 3 by a predetermined distance and disposed in a direction of the screen. Also, the control electrode 4 is faced with the rear electrode 2 and formed of a conductive plate in which passing holes are disposed at each predetermined distance in a horizontal direction and formed on a horizontal line facing each filament cathode 3 by a predetermined distance.
The signal modulation electrode 5 includes a row of conductive plates, each of which is arranged on a position facing each passing hole of the control electrode 4 and spaced apart from the control electrode 4 by a predetermined distance. At this time, each conductive plate is thin and long in a vertical direction. Each conductive plate of the signal modulation electrode 5 has passing holes formed in the same plane on a position facing each passing hole of the control electrode 4.
The focus electrode 6 is formed of a conductive plate having passing holes formed on each position facing each passing hole of the signal modulation electrode 5. The horizontal deflection electrode 7 includes two conductive plates meshed with each other on a sectional portion and spaced apart by a predetermined distance on the same plane.
Further, the vertical deflection electrode 8 also includes two conductive plates meshed with each other on a sectional portion and spaced apart by a predetermined distance on the same plane.
Generally, all of the above-described electrodes are manufactured using an Invar (Fe-Ni alloy) in order to prevent an image quality from being degraded due to a thermal deformation. Each of the control electrode 4, the signal modulation electrode 5, the focus electrode 6, the horizontal deflection electrode 7 and the vertical deflection electrode 8 is joined with an insulating adhesive.
FIG. 2 is a view explaining a phosphor screen of the conventional color flat panel display.
Referring to FIG. 2, a phosphor screen 15 is formed on the front glass 9 and R, G and B phosphors 12 are coated on an inner side of the front glass 9. Black matrixes (BM) 14 are formed between the phosphors 12.
In addition, a metal back 13 is formed on the phosphors 12 to thereby reflect and project a light generated by the phosphors 12 on the front glass 9.
On the basis of the above structure, an operation of the conventional color flat panel display will be described below with reference to FIGS. 1 and 2.
If a voltage is applied to the filament cathode 3, electrons are emitted. At this time, the filament cathode 3 is heated by passing a current therethrough in order to easily obtain the electron emission.
The electrons emitted from the filament electrode 3 are divided into multiple parts by the passing holes of the control electrode 4 and its amount is controlled.
A passing amount of the electron beam 11 passed through the control electrode 4 is controlled corresponding to an image signal at the signal modulation electrode 5.
The electron beam 11 passed through the signal modulation electrode 5 is focused at the passing holes of the focus electrode 6 due to a static lens effect. The electron beam 11 is deflected by passing both the horizontal deflection electrode 7 and the vertical deflection electrode 8 and then it is scanned to the phosphor 12 of corresponding unit cell 10, thereby displaying a desired image.
At this time, a voltage applied to the electrode adjacent to the screen is maximally of 600 V and a voltage of the screen is approximately of 10,000-14,000 V.
In other words, since a high voltage of approximately 10,000 v is applied to the metal back 13, the electron beam 11 is accelerated to a high energy and collided against the metal back 13, thereby light-emitting the phosphor 12.
FIG. 3 is a view showing a structure of the vertical deflection electrode 8 in the conventional color flat panel display.
As shown in FIG. 3, the vertical deflection electrode 8 is made in a structure that two conductive plates 8a and 8b are meshed with each other on a sectional portion and spaced apart by a predetermined distance on the same plane.
In other words, it positive and negative voltages are applied to the conductive plates 8a and 8b respectively, an electric field is generated, and the electric field causes the electric beam to be deflected, thereby achieving a vertical deflection.
In addition, a horizontal deflection is achieved in the horizontal deflection electrode 7 by the same principle as the vertical deflection.
FIG. 4 is a view explaining an assembly process of the electrodes, in which a pre-sintering state and a post-sintering state are shown.
Explaining the assembly process of the electrodes with reference to FIG. 4, crystalline glass rods 22 of a relatively low melting point are inserted into both sides of amorphous glass rods 21 of a relatively high melting point between the electrodes, and then the sintering process is carried out. Consequently, the crystalline glass rods 22 are melted to wrap the amorphous glass rods 21, thereby acting as an adhesive.
In other words, the amorphous glass rods 21 are made from crystal that is the main raw material, and has a softening temperature of approximately 550° C. If the amorphous glass rods 21 are pressed at approximately 450° C. while being sintered, the crystalline glass rods 22 that have a melting point lower relative to the amorphous glass rods 21 are melted, so that both electrodes are bonded.
At this time, a gap between both electrodes is maintained as much as a diameter of the amorphous glass rod 21, and thus the amorphous glass rods 21 serve as the spacer.
In the meanwhile, in order to improve the brightness uniformity of an image that is the most important factor in reproducing a moving picture, it is the most important to allow the gap between the electrodes to be maintained at a constant size.
In particular, in case the gap between the electrodes in a color flat panel display is changed, the image size of the electron beam is changed too, so that the brightness uniformity is not obtained and a whole image quality is deteriorated.
Accordingly, it is necessary to maintain the gap between the electrodes at a constant size. The amorphous glass rods 21 are made from crystal not having a variation in the shape or diameter at an approximately 450° C. Then, since the cost of the amorphous glass rods 21 corresponds to 70% of the overall cost of all the electrodes, the manufacturing costs of the color flat panel display increase.
In addition, it is requested to arrange the pair of crystalline glass rods 22 at both sides of the amorphous glass rods 21 during the bonding process of the respective electrodes. In order to bond all the electrodes, working time and the number of the bonding process increase, so that there occurs a problem in that the manufacturing costs increase.